August 13, 2007: AAVSO Alert Notice 348 (issued April 6, 2007) included the request from Dr. Gordon Sarty, University of Saskatchewan, for AAVSO assistance in observing four (4) High Mass X-ray Binaries (HMXBs) in support of his spectroscopic observations with the Dominion Astrophysical Observatory (DAO) 1.85-m Plaskett telescope, in Victoria, BC, Canada. Dr. Sarty has obtained additional observing time on these objects and is requesting our continued assistance over the next several weeks.

Dr. Sarty asks our observers to obtain IVBR photometry (in that order of preference) from now through September 2007. Observations with the DAO Plaskett telescope will be made August 20 to September 3 and will be measured to find the radial velocities. "The object is to determine the orbital periods of the HMXBs. Optical photometry will also reveal other periods and variation due to mass transfer, pulsations, and other effects. The availability of photometry will be very valuable for interpreting the spectroscopic data.

"HMXBs consist of an exotic neutron star or black hole in orbit around a more massive ordinary (O or B type) star. Mass is transferred from the ordinary star to the exotic star through a variety of mechanisms, including accretion disks (to the exotic star), decretion disks (from a rapidly spinning ordinary star), and high stellar winds. These mass transfer processes cause many HMXBs to be variable stars. The true distribution of HMXB orbital periods is not yet known because the orbital periods of many are years in length. Thus amateur observations of HMXBs will be very valuable for finding the true distribution. More information about HMXBs will be published in an article in JAAVSO Vol. 35, No. 2." A preprint of that article may be found at

As mentioned in Alert Notice 348, please follow the observing instructions given on the chart web page and on the charts and submit your results directly to the AAVSO International Database. Also as before, Dr. Sarty says that contributors of useful data will be offered authorship on the publications resulting from this observing campaign, and he asks that any questions about this observing campaign be sent to him at gordon.sarty@usask.ca.

Your observations of these bright HMXBs are extremely important both to the success of this research and to increasing the fundamental knowledge of this class of objects. Many thanks for your efforts and your astronomical contributions.